Some aircraft have the capability to communicate with satellites in various earth orbits, such as geosynchronous (GEO), low earth orbit (LEO), and polar orbit. Transmission of high data rates between aircraft and the satellites at a low power level requires a highly directive antenna with a large aperture area. Such a directive antenna strives to maintain accurate positioning to point the antenna in the direction of the satellite. The satellite is in constant motion in orbit around the earth. As the aircraft moves, it is subject to changes in latitude, longitude, and altitude. The aircraft's attitude, measured in roll, pitch and yaw, can also change relative to the satellite. A gimbaled antenna pedestal can be used to compensate for the movement of the satellite and changes in velocity, position, and attitude of the aircraft and allow the antenna mounted on the aircraft to maintain its focus on a satellite.
Most aircraft are composed of metal skins, such as aluminum. The metal skins can create a Faraday cage inside the aircraft which can substantially decrease any electromagnetic signals. To overcome this, the antenna and pedestal are usually mounted on the exterior of the aircraft.
The environment outside an aircraft, however, is not hospitable to most large area antennae. Antenna apertures typically require a specific large area shape to capture a desired electromagnetic signal. As a result, the required antenna shape is usually not very aerodynamic. The relatively high velocity air flow while an aircraft is in flight can also interfere with the movement of an antenna that is required to maintain the focus of the antenna on the satellite. Also, temperatures can often vary over one hundred degrees Celsius as an aircraft ascends and descends. The rapid change in temperature can cause problems with electrical systems associated with the antenna and pedestal.
Enclosures can be used to overcome the environmental problems associated with placing antennae on the outside of an aircraft. Antenna enclosures, called radomes, are constructed out of materials which are substantially transparent to electromagnetic radiation. Radomes should be as small as possible to minimize aerodynamic drag. A flattened radome can further minimize drag. However, accurate pointing and control are desired to be maintained as the aircraft rolls, pitches, and yaws in normal flight. It is desirable to control the movement of an antenna in a radome mounted on an aircraft to allow the antenna to be positioned to transmit and receive maximum power signals from a satellite to enable a communications link with minimal disruptions.